More than 500 million people in the world have some form of disability, ranging across varying forms of mental, physical, and sensory disabilities. Society has implemented a number of real world methods to provide better access for people of varying disabilities. For example, handicapped parking spaces have been created to allow disabled persons to park closer to commercial businesses. Society has also implemented audible noises from sign-posts to alert the visually impaired that it is safe to cross the street. Moreover, low-gradient ramps have been created to make entering a multilevel building easier for persons confined to wheelchairs or whom have difficulties with stairs.
A virtual universe (VU) is an interactive simulated environment accessed by multiple users through an online interface. Users inhabit and interact in the VU via avatars, which are a user's representation of himself or herself. These representations can be in the form of a three-dimensional model, a two-dimensional icon, a text construct, a user screen name, etc. Although there are many different types of VUs, there are several features many VUs generally have in common. These features include, for example,                Shared Space: the VU allows many users to participate at once;        Graphical User Interface: the VU depicts space visually, ranging in style from 2D “cartoon” imagery to more immersive 3D environments;        Immediacy: interaction takes place in real time;        Interactivity: the VU allows users to alter, develop, build, or submit customized content;        Persistence: the VU's existence continues regardless of whether individual users are logged in; and        Socialization/Community: the VU allows and encourages the formation of social groups such as teams, guilds, clubs, cliques, housemates, neighborhoods, etc.        
Disabled users participating in VUs are at a disadvantage due to their disabilities, which can limit their ability to fully experience and interact within a VU. For example, users who have visual or auditory disabilities may be unable to interact with objects, structures, or avatars in a VU, which are largely based on sight and sound. Thus, a user with poor eyesight may be unable to navigate steps or open doors in a VU, which limits the extent to which the user can participate in the VU.